1. Field of the Invention
The present invention generally relates storage systems on computers and more particularly, to storage systems enabled to expand from small to large configurations, and to management methods thereof.
2. Discussion of Background
As explained in JP-A No.242434/2000, along with the penetration of IT systems in corporations and spread of the cooperation of those corporations through the IT systems due to the progress of the Internet, the roles of the storage systems for storing data processed in such IT systems is becoming important more and more as the core of the IT systems. And, to cope with such the roles, there have been proposed various types of storage systems enabled to correspond to small to large configurations.
For example, one of such the storage systems is a conventional storage system structured as shown in FIG. 2. This storage system comprises a plurality of channel IF units, each used for sending/receiving data to/from a server 3, a plurality of disk IF units 16, each used for sending/receiving data to/from hard drives 2, a cache memory unit 14 for storing data to be stored in the hard drives 2 temporarily, and a control memory unit 15 for storing control information (ex., information related to the data transfer control in the storage system 8 and management information of data to be stored in the hard drives 2) related to the storage system 8. In the storage system, an interconnection 41 is used for the connection between the plurality of channel IF units/disk IF units and the plurality of cache memory unit 15 while another interconnection 42 is used for the connection between the plurality of channel IF units 11/disk IF units and the control memory unit 15. Each of the interconnections 41 and 42 is generally configured by common buses or switches.
Consequently, the storage system 8 is configured so that the cache memory unit 14 and the control memory unit 15 are accessed from all the channel IF units 11/disk IF units 16.
Each channel IF unit 11 includes an interface (host IF 104) with the server 3, a microprocessor 103 for controlling the input from output to the server 3, a memory access unit 106 for controlling the access to the cache memory unit 14, and a memory access unit 107 for controlling the access to the control memory unit 15. Each disk IF unit 16 includes an interface (disk IF 105) with the hard drives 2, a microprocessor 103 for controlling the input from or output to the hard drives 2, a memory access unit 106 for controlling the access to the cache memory unit 14, and a memory access unit for controlling the access to the control memory unit 15. Each disk IF unit 16 also executes the RAID function.
In the above storage system 8, the channel IF units 11 for controlling data transfer to/from the servers 3 and the disk IF units 16 for controlling the data transfer to/from the hard drives 2 are separated from each other and the data transfer between the channel IF units 11 and the disk IF units 16 is controlled through the cache memory unit 14 and the control memory unit 15, so that it has been possible to change the number of both of the channel IF units 11 and the disk IF units flexibly. This is why the storage system 8 has been enabled to correspond to small to large scale configurations.
And, in the conventional technique disclosed in JP-A No.242434/2000, as shown in FIG. 21, a plurality of disk array units 4 are connected to a plurality of servers 3 through a disk array switch 5 and the system configuration management unit 60 connected to the disk array switch 5 and the disk array units 4 manages those disk array units 4 integrally as one storage system 9.
In large scale corporations such as banks, securities and brokerage firms, telephone companies, etc., a marked tendency to integrate their computers and storages having been dispersed in places into computer systems and storage systems and placed in data centers is seen lately, thereby reducing the costs of the operation, maintenance, and management of those systems.
On the other hand, a tendency to suppress the initial investments to IT systems and expand the system scales according to the expansion of business scales is also seen in those corporations under the depression started by the collapse of economic bubble and accelerated by the collapse of IT bubble and the terrorism occurred in the USA. And accordingly, the storage systems have been required to have a scalability of both cost and performance that enable each storage system to expand with a reasonable investment in accordance with an expected business scale.
According to the conventional technique shown in FIG. 2, the data transfer between all the channel IF units 11 and all the disk IF units 16 is controlled through the cache memory unit 14 and the control memory unit 15, thereby data is read/written from/to the servers 3 to/from the hard drives 2. The access load of all the channel IF units 11 and all the disk IF units 16 is thus concentrated in the cache memory unit 14 and the control memory unit 15.
And, the required performance of such the storage system (the input/output frequency of data per unit time and the data transfer rate per unit time) is becoming higher and higher every year. To meet such the requirement, therefore, the data transfer rate of both of the channel IF unit and the disk IF unit is also required to be improved.
As described above, because the data transfer between all the channel IF units 11 and all the disk IF units 16 is controlled through the cache memory unit 14 and the control memory unit 15 in the conventional technique, the access load to the channel IF units 11 and the disk IF units 16 increases when the data transfer rate of the channel IF units 11 and the disk IF units 16 is improved. And, such the increase of the access load becomes a bottleneck that makes it difficult to improve the performance of the storage system 8. This has been a problem of the conventional technique.
On the other hand, it is possible to improve such the access performance that enables both the cache memory unit 14 and the control memory unit 15 to be scaled up significantly to cope with the above increase of the access load. In this case, however, each of the cache memory unit 14 and the control memory unit 15 comes to be managed as a shared memory space to enable the units 14 and 15 to be accessed from all the channel IF units 11 and all the disk IF units 16. Therefore, if the cache memory unit 15 and/or control memory unit 15 is scaled up significantly, it becomes difficult to reduce the cost of the storage system 8 in a small configuration, thereby it becomes difficult to provide small configuration systems at low prices. This has been another problem of the conventional technique.
Furthermore, in the conventional technique shown in FIG. 21, it is possible to increase the number of disk array units 4 and the servers 3 that are connectable by increasing the number of ports of the disk array switch 5 and connecting a plurality of disk array switches 5 in multiple steps, so that the storage system is realized so as to be enabled to correspond to small to large configurations scalably. However, because each server 3 accesses each disk array unit 4 through the disk array switch 5 in that case, the disk array switch 5 is required to transform the server—disk array switch protocol to a protocol used in the disk array unit 5 through its interface unit with the server 3, as well as to transform the protocol used in the disk array unit 5 to the disk array switch—disk array unit protocol through its interface with the disk array unit 4 in the disk array switch 5. And accordingly, the response performance of the conventional technique becomes lower than the direct access to the disk array unit without using the disk array switch. This has been a problem of the conventional technique.
Under such circumstances, it is an object of the present invention to provide a storage system enabled to expand from small to large scale configurations flexibly at a reasonable price/performance appropriately to the expected system scale.
More concretely, the object of the present invention is to provide a storage system having a scalability of both cost and performance so as to correspond to small to large scale configurations by eliminating the bottleneck in the shared memory of the conventional storage system and reducing the costs of small configuration systems.